There is an urgent need for novel means of diagnosing, prognosing, and treating prostate cancer, the second leading cause of cancer-related deaths among men. The recent landmark discovery of extracellular small RNAs has opened the door to their use as biomarkers and their manipulation as a therapeutic strategy. However, to reach that potential more needs to be known about their origins and functions. Without such knowledge it will be exceedingly difficult to translate the phenomenon of their existence to useful clinical interventions. The long-term goal of this lab is to understand how microRNA-messenger RNA networks regulate prostate cancer progression and use that knowledge to drive novel assessments and treatments for the disease. The objective here is to evaluate the source, form, destination, and function of extracellular microRNAs associated with pathological progression of prostate cancer. The central hypothesis is that microRNA secretion is actively regulated by tumor pathways that drive prostate cancer progression and that these microRNAs act in a paracrine fashion communicating between different cell types within the tumor niche. This hypothesis derives from preliminary data identifying a novel microRNA signature in serum of patients who are found to have worse disease upon post-surgical analysis ofthe prostate than predicted based on pre-surgical parameters. Importantiy, the specific microRNAs found in the serum of these patients combined with evaluation of their levels in the tumor cells suggest that the microRNAs become actively and selectively secreted upon progression. Based on these preliminary data, the following specific aims are proposed: 1) Uncover the basis for the microRNA signature associated with pathological progression ofthe prostate tumor, 2) Determine whether different tumor causing pathways will produce common or distinct serum signatures associated with tumor progression, and 3) Analyze potential roles for the secreted microRNAs in altering the tumor niche through intercellular communication. In aim 1, matching tumor and serum samples from human patients will be evaluated by novel quantitative approaches to measure the microRNAs present and the form of secretion. In aim 2, mouse models will be used to evaluate the effect of distinct tumorigenic pathways on the repertoire and form of microRNAs released and their response to small molecule inhibitors. In aim 3, the function of microRNAs secreted from human tumor cells on the neighboring stromal tissue will be dissected. The proposal is highly significant as it will uncover novel paradigms of how microRNAs are induced, sorted, and secreted from the tumor cells as well as where they go and how they function at their destination. Such knowledge will provide greatiy improved insights into how to use extracellular microRNAs in the evaluation and treatment of prostate cancer. Furthermore, the proposal is expected to find paradigms that are more broadly applicable to multiple systems, which will be directiy tested together with other projects within the proposed U19 Center.